I think Alex could've embarrassed Piers by having him state or stating the known number of AR's in civilian hands.
And that under Piers' logic, the number of AR's in circulation times the number of people killed by those weapons in mass murders should equal much more than 20 people killed.
As many AR's that are in citizens' hands, and as "dangerous" as they say they are, there should be hundreds of thousands killed everyday.
Most people claim to be "good" at math and maybe this would've put this in a better perspective.
Of course this always come up after the fact.

__________________
"You can't get 'em all Josey."
"That's a fact".
"Well how come you doin' this then?"
"Cause I got nothin' better to do."